Silicone lubricating oil composition containing ester for improved lubricity and thermal stability



r 2,950,250 1C Patented A g- 23, 1960 SILICONE LUBRICATING 01L COMPOSITION CONTAINING ESTER FOR IMPROVED LU- BRICITY AND THERMAL STABILITY Morton Z. Fainrnan, Chicago, 111., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana N Drawing. Filed Feb. 29, 1956, Ser. No. 568,436

Claims. (Cl. 252-49.'6)

This invention relates to improvements in synthetic lubricant compositions and more particularly relates to improved silicone polymer lubricants having improved lubricity properties and good thermal stability.

Silicone oils used as lubricants possess good thermal stability and have a favorable viscosity-temperature relation or viscosity index (V.I.). They also possess desirable high flash point and low pour point characteristics. However, the silicone oils have poor lubricity prop erties which make them poor lubricants under boundary lubricating conditions, particularly for ferrous metal hearing surfaces. As a corollary to the poor lubricity, the silicones permit excessive wear. It is an object of this invention to provide a silicone lubricant having improved lubricity properties. Another object of the invention is to provide a silicone lubricating oil composition having thermal stability, a high viscosity index and improved lubricity characteristics. Other objects and advantages of the invention will become apparent from the following description thereof.

In accordance with the herein-described invention, the foregoing objects can be attained by incorporating in silicone oil lubricants from about 5% to about 75%, and preferably from about to about 45% of an ester of a straight chain aliphatic carboxylic acid of from about 4 to about 18 carbon atoms and a polyhydric alcohol free of beta hydrogen; that is, containing no hydrogen on the beta carbon atom. Illustrative of such esters are those having the general formula:

in which R and R are the same or difierent straight chain alkyl radicals of from 4 to about 18 carbon atoms, R and R are selected from the group consisting of hydrogen, or alkyl radicals of from 1 to 4 carbon atoms and mixtures thereof, R is selected from the group consisting of an alkyl radical of l to 6 carbo'n atoms, or a hydroxy methyl radical, and R is selected from the group consisting of an alkyl radical of 2 to about 12 carbon atoms or a hydroxy methyl radical. The R and R groups may be the same or different.

Polyhydric alcohols free of beta, hydrogen can be readily prepared to give a structure derived from neopentane. Acetaldehyde is treated with '5 equivalents of formaldehyde in an aqueous solution of calcium hydroxide at 15-45" to give pentaerythritol according to the following steps:

C(OH2OH)4+C8(OOCH)2 By choosing a diiferent aldehyde or ketone as starting material, we obtain other polyhydric alcohols. l1lustrative of such polyhydric alcohols free of beta hydrogen are:

( CHIOH H3C-(J-CH3 CHaOH Neopentyl glycol GHnOH HaC-C-CH20H CHZOH Trimethylolethane H CHaOH HaC-(B-G-CHgOH H CH20H Trimethylolpropane OHzOH HOHzC-O-CHrOH CH20H Pentaerythritol CHzOH HaCr-C-CzHs CHzOH 2-butyl-2-ethyl-l,B-propenediol Examples of straight chain alkyl carboxylic acids with which polyhydric alcohols of the above type may be esterified are n-butyric acid, n-pentanoic acid, n-octanoic acid, n-nonanoic acid( pelargonic acid), n-decanoic acid (caprlc acid), lauric acid, myristic acid, stearic acid, etc. The esters of straight chain alkyl carboxylic acids and polyhydric alcohols free of beta hydrogens po'ssess high viscosity index, high flash point, and good thermal stability characteristics as compared to the esters of branched chain acids. The differences in these physical properties between the esters of straight chain acids and the esters of branched chain esters are illustrated by the data in Table I.

TABLE I Pour Flash Viscosity, Cs. Acid b Point, Point, Viscosity F. F. Index NEOPENTYL GLYGOL TRIMETHYLOLETHANE TRIMETHYLOLPROPANE Footnotes at end of table.

- Melting point, F. 1 b n=straight chain acids. br=branched chain acids.

In addition to the above physical properties, the esters of the straight chain acids possess better lubricity characteristics than do the esters of the branched chain acids. This is demonstrated by the data in Table II. The static (,u coeflicient of friction and the kinetic (,u coefiicient .of friction were obtained on stick-slip machine described in the article by M. E. Merchant on Characteristics of Typical Polar and Non-Polar Lubricant Additives Under Stick-Slip Conditions in Lubrication Engineering, June 2, 1946, pp. 56-61. The described apparatus provides a means for determining the kinetic friction (,u and the static friction (,u between two metal surfaces and thereby a'measure of the lubricity of the lubricant under boundary lubrication conditions. Smooth sliding; indicative of good lubricity, occurs when ,u /p is 811118110 or less than 1., When the value of t /c is greater than 1, sticking occurs. 7 a

TABLE II properties of polyhydrio-alcohol Boundary lubrication e 17 esters COEFFICIENT or FRICTION Acid. Static, Kinetic, p [l /[1k NEO;EENTYL GLYCOL Ill-C9 0. 131 0. 142 0. 92 0. 120' V i 0. 137 0. 88 0. 183 0. 181 1. 01 i o. 213 I 0.192 g 1.11 U. 188 0. 184 1. 02 0. 187 0.184. W1. 02

TRIMETHYLOLETHANE h.

0. 112 0. 135 0. 83 O. 126 0. 1 2, ,0. 89 0. 113 0. 131 U. 86 O; 121' 0. 142 0; 85'

0. 092 O. 118 0. 70 0. 186 O. 183 1. 02 O. 205 O. 181 1. 13 0. 181 17 7 1. 02 0.183 h, 1.01

Acid Static, ,1, Kinetic, p [L /[1k 2BUTYL-2-ETHYL-L3-PROPANEDIOL I have found that the esters of straight chain carboxylic acids and polyhydric alcohols free of beta hydrogens efiectively increase the lubricity of silicone oils. The silicone oils are essentially polyorgano silicones (sometime referred to as siloxanes) which may be represented by the general structure carbon radical, such as straight or branched chain alkyl,

' aryl, alkaryl or aralkylradicals and n is greater than 1.

Examples ofsuch radicals are methyl, ethyl, ethyl-methyl, phenyl, tolyl, phenyl-methyl, ethyl-'phenyl, etc. The commercial silicone oils are essentially polymethylsiloxanes,

polyethyl siloxanes and poly (methyhphenyl) siloxanes. The molecular weights of silicone oils vary from about 200, for light-oils to about. 1,000 or more for the viscous oils.

The efiectiveness of the herein-described esters of the present invention in improving the lubricity characteristics of silicone oils isrillustrated by the data in Table III.

TABLE HI Coefficient of Friction Static, Kinetic, llm.

P! i k Silicone oil 0.299 0. 294 1.02 Silicone 0il+10% trimethylopropanetri-n-nonoate 0. 153 0.170 0. Silicone oil+20% trimethylolpropanetri-n-nonoate 0. 141 0. 0. 87 Silicone oil-H07 neopentyl-di-nnonoate--- 0. 160 0. 174 0. 92 Silicone o nonoate 0.150 0.161 0.93 Silicone oil+20% e neopentyl di-brnonoate 0. 225 0. 223 l. 01 Dioctyl adipate 0.262 0. 174 1. 51 20% trimethylolpropane-tri-n-nouoate+ 80% dioctyl adipate 0.206 0.195 1.06

50% trimethylolpropane-tri-n-nonoate+ 50% dioctyl adipate 0. 0. 194 1. 01

The data in Table III demonstrate that as little as 10% of the esters of a polyhydric alcohol free of beta hydrogen and a straightchain carboxylic acid is efiective in so improving the lubricity of silicone oils to give a smooth sliding lubricant, i.e. reduces the coeflicient'of friction value of pu /[4 from 1.02 (sticking) to a'valueless than 1.00 (smooth sliding); However, the lubricity of other synthetic lubricating oils are not similarly aifected. As

shown by the data inTable HI, the coeflicient of friction value of t /p fordioctyl adipate'is' not reduced to a value of 1 or less even by the addition of as much as 50% of trimethyolpropane-tri-n-nonoate. g a

The lubricant compositions of silicone; oils and the esters of the present invention can, if desired, contain one or more other additives such as oxidation inhibitors, rust inhibitors, detergents, etc.

less otherwise stated.

The percentages given herein are weight percentages un- I claim: 1. A lubricant composition comprising at least 25% of a silicone oil having the general structure in which R R and R are radicals selected from the group consisting of methyl, ethyl, ethyl-methyl, phenyl, tolyl, phenyl-methyl, ethyl-phenyl radicals and mixtures thereof and from about 5% to about 75% of an ester of a straight chain aliphatic carboxylic acid of from about 4 to about 18 carbon atoms and a polyhydn'c alcohol free of beta-hydrogen, said ester having the general formula l RGOCH R7C-R5 R- OI-H in which R and R are straight chain alkyl radicals having from 4 to about 18 carbons, R and R are constituents selected from the group consisting of hydrogen, alkyl radicals containing from 1 to 4 carbon atoms and mixtures thereof, R is a constituent selected from the group consisting of an alkyl radical having from 1 to 6 carbon atoms and a hydroxy methyl radical, and R is a constituent selected from the group consisting of an alkyl radical having from 2 to about 12 carbon atoms and a hydroxy methyl radical.

2. A lubricant composition comprising at least 25 of a silicone oil having the general structure in which R R and R are radicals selected from the group consisting of methyl, ethyl, ethyl-methyl, phenyl, tolyl, phenyl-rnethyl, ethyl-phenyl radicals and mixtures thereof and from about 5% to about 75% trimethylolpropane-tri-n-nonoate.

6, 3. A lubricant composition comprising at least 25% of a silicone oil having the general structure in which R R and R are radicals selected from the group consisting of methyl, ethyl, ethyl-methyl, phenyl, tolyl, phenyl-methyl, ethyl-phenyl radicals and mixtures thereof and from about 5% to about trimethylolethane-tri-n-decanoate.

5. A lubricant composition comprising at least 25% of a silicone oil having the general structure in which R R and R are radicals selected from the group consisting of methyl, ethyl, ethyl-methyl, phenyl,

tolyl, phenyl-methyl, ethyl-phenyl radicals and mixtures thereof and from about 5% to about 75% 2-butyl-2- ethyl-l,3-propanediol-di-n-octadecanoate.

References Cited in the file of this patent UNITED STATES PATENTS 2,471,850 Wilcock May 31, 1949 2,561,178 Burkhard July 17, 1951 2,597,045 Wilcock et a1. May 20, 1952 2,798,083 Bell et al. July 2, 1957 FOREIGN PATENTS 715,933 Great Britain Sept. 22, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,950,250 August 23 1960 Morton Z. Fainman It is hereby certified that error appears in the printed specification oi the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 58 Table I, first column thereof, for "br-C- read Ion-C column 3., lines 29 and 230 for "Lubrication Engineering" read Lubrication Engineering 2 column 5 lines 11 and 43, and column 6, lines l0 21, and 33, after thereoi" each occurrence, insert and n is greater than 1 Signed and sealed this 4th day of April 1961,

(SEAL) Attest: ERNEST W. SWIDER PQXWK ARTHUR W. CRGCKER Attesting Oficer A ting Commissioner of Patents 

1. A LUBRICANT COMPOSITION COMPRISING AT LEAST 25% OF A SILICONE OIL HAVING THE GENERAL STRUCTURE 